1. Field of the Invention
The invention relates to a protection circuit, and more specifically to a protection circuit capable of limiting a power source of an electronic device outputting a predetermined range of current for charging a peripheral unit.
2. Description of the Related Art
Electronic devices typically generate an excessive starting current and voltage, when connecting or disconnecting a peripheral component. These actions affect normal equipment operation and potentially damage the electronic devices.
Conventional protection circuits fabricated by separated components have drawbacks of low reliability and high cost for maintenance. To meet special application, many systems provide protection circuits for avoiding damages of ESD, surge current, overcurrent, undervoltage and overvoltage, and for carrying out current limiting to satisfy various requirements. Some protection circuits are for meeting special industry standards, such as UL, USB, IEEE, CSA or IEC. The protection circuits used for protecting equipments or operators typically have an adjustable current limiting function for avoiding equipment damages when plugging in or out peripheral components from the equipments. Surge current protection is the basic requirement for a current-limiting circuit to prevent surge current induced by a large capacitive load plugging in the equipment. Additionally, the current limiting function can also reduce the output of a power source to prevent generating arc when connecting a peripheral.
Examples of peripheral units for general communication used include global system for mobile card (GSM), general packet radio service card (GPRS), both devices require higher power for wireless transmission and therefore many large capacitive loads, for the power amplifiers to carry out wireless transmission, are built in the peripheral units. When a peripheral unit with large capacitive loads plugs in an electronic system such as a personal digital assistant, notebook or personal computer, the large capacitive loads may induce high charging current flowing from the power source installed in the electronic system to the peripheral unit and cause damages and instability.
Therefore, the invention provides a small fast inexpensive protection circuit. The protection circuit can additionally prevent high current, due to a short circuit.